This invention relates to bearing blocks of the type in which a bearing supporting bore is formed with half of the bore in a support structure and the other half in a bearing cap which is secured to the support structure, in which the cap must be precisely refitted to the support structure after machining operations on the bore are carried out. In particular, this invention relates to a sintered powder metal bearing cap having features for providing precise relocation of the cap relative to the support structure.
The essential function of a bearing cap is to retain and locate a rotary shaft, or a bearing for a rotary shaft which in turn retains and locates the shaft, relative to a support structure. For example, the main bearing cap of an engine bolts to a bulkhead of the engine crankcase and together with the bulkhead retains and locates the crankshaft journal in place while the crankshaft is rotating. The crankshaft journal runs against two half shell bearings which are fitted to the main bearing cap and the engine bulkhead semi-circular bores, respectively.
In this case, for vibration free, low friction and quiet running, the roundness of the bore produced by the main bearing cap and the bulkhead is very important. This roundness is achieved by a machining operation called line boring. The main bearing caps are bolted to the bulkheads of the engine block, and then a boring bar fitted with a cutting tool is used to machine the bores in the assembly. This ensures the two half rounds formed by the main bearing cap and the bearing block form as near to a perfect circle as possible. A finishing operation involving a grinding hone is often used to achieve the extremely fine tolerances needed for quiet running and efficient engine performance.
However, to install the crankshaft, it is necessary to remove the main bearing caps from the engine block. After the crankshaft is put in place, the main bearing caps must be re-positioned on the bulkhead so that they are replaced in the identical position they occupied during the line boring operation. Any deviation from that original position produces an out-of-round condition that, in turn, leads to vibration, noise and possibly stiff, high friction crankshaft operation.
U.S. Pat. No. 6,086,258 entitled “Precisely Repositionable Bearing Cap” which issued on Jul. 11, 2000, and PCT International Patent Application Publication No. WO2007/081715 entitled “Precision Location and Low Force Repositioning of Powder Metal Components” which published on Jul. 19, 2007, are hereby incorporated by reference as if set forth herein in their entirety for all purposes. This patent and international patent application publication describe repositionable powder metal bearing caps having bosses around the bolt holes. These bosses extend from the bottom of the feet of the bearing cap into counterbores of the structure to which the bearing cap is assembled. However, forming these assemblies can potentially require large forces to press the bearing cap initially into the receiving structure and to withdraw the bearing cap for insertion of the crankshaft. Unfortunately, there also exists the possibility that if the parts are not joined closely enough to one another that foot fretting may develop under vibration.
Hence a continuing need remains for bearing caps that can be located relative to a component to which the bearing cap is joined without the implementation of excessive force and with a reduction in the occurrence of foot fretting.